https://en.m.wikipedia.org/wiki/False_vacuumTLDR: A ball rolling down a hill will tend to settle into the lowest energy state. If it perches itself on an outcropping of rock, for example, it is in a false ground state. Meaning, it only appears to be in its true ground state. An earthquake could dislodge it and it would continue tumbling down to its true ground state, or state of lowest energy. A false vacuum state is the same thing, but with the universe. Basically, if we are currently in a false vacuum state, a burst of tremendous energy could send it tumbling down to its true vacuum state, thereby obliterating the known universe.
Also, it's not clear which state our universe is in. It could be in a true vacuum state, or a prolonged false vacuum state. So, the ball rolling down the hill could have settled into a space where no force has been able to dislodge it.